On the non-blocking conditions of self-routeing multistage interconnection networks

This paper studies the non-blocking conditions of a generic N × N multistage interconnection network, such as an omega network or an n-cube network, in which only one path connects any inlet to each outlet and different I/O paths can share interstage links. It is widely known that any of these networks is non-blocking for a compact and monotone pattern of k ≤ N I/O paths. Recently it has become very important to show the network non-blocking property for permutation sets, wider than the compact and monotone, which are usually encountered in broadband ATM networks. By using a new approach based on the concept of distance between I/O paths, we show here that these networks are non-blocking for a set of I/O paths obtained by shifting cyclically the inlets of a compact and monotone pattern of I/O paths by an arbitrary number of steps.     

Buffering-deflection tradeoffs in optical burst switching

A very important issue in optical burst switching (OBS) networks is the excessive burst drop when no suitable network resources are found during path reservation. In this study, a network scenario is evaluated in which AWG-based optical nodes are used as burst router nodes within the optical network. The two classical solutions to solve the burst contentions on the channels outgoing from the node are considered, that is, either based on buffering within the node, or by exploiting deflection routing. A performance evaluation is carried out to evaluate and compare these solutions for different network topologies with different node and traffic parameters. Our main contribution is to set numerical tradeoffs between burst deflection through the network and buffering in the node, so that a guidance in optical network design is provided where node buffering is inherently technologically limited.     

Slot Synchronization of a WDM Packet-Switched Slotted Ring

In this paper, we present two different strategies of slot synchronization in wavelength-division-multiplexing (WDM) packet-switched slotted-ring networks. Emphasis is given to the architecture behind the WDM optical network demonstrator over rings (WONDER) project, which is based on tunable transmitters and fixed receivers. The WONDER experimental prototype is currently being developed at the laboratories of Politecnico di Torino. In the former strategy, a slot-synchronization signal is transmitted by the master station on a dedicated control wavelength; in the latter, slave nodes achieve slot synchronization aligning on data packets that are received from the master. The performance of both synchronization strategies, particularly in terms of packet-collision probability, was evaluated by simulation. The technique based on transmitting a timing signal on a dedicated control wavelength achieves better performance, although it is more expensive due to the need for an additional wavelength. However, the technique based on aligning data packets that are received from the master, despite attaining lower timing stability, still deserves further study, particularly if limiting the number of wavelengths and receivers is a major requirement. Some experimental results, which were measured on the WONDER prototype, are also shown. Measurement results, together with theoretical findings, demonstrate the good synchronization performance of the prototype.     

Nonblocking architectures for ATM switching

General models for a class of nonblocking architectures of asynchronous transfer mode (ATM) switches are described. Hardware aspects are discussed to show the implementation feasibility of the proposed switch architectures by means of the current technology. Performance issues are studied to point out the traffic bottlenecks of the different structures. It is shown that the classification of queueing is the main concept that enables the classification of nonblocking ATM switches. Three main packet queueing strategies can be adopted in the switching fabric: input queueing, shared queueing, and output queueing. Switch architectures adopting only one of these strategies are described. The ways in which two strategies can be jointly adopted in a switching fabric to result in the mixed queueing strategies input-output queueing, input-shared queueing, and shared-output queueing are also discussed     

Multi-wavelength switching in IP optical nodes adopting different buffering strategies

The paper addresses the topic of long-haul optical networking for the provision of large-bandwidth IP services. A class of optical packet switching architectures is considered which adopts an arrayed wavelength grating device as packet router. The architecture performs slotted packet switching operations and fully exploits the wavelength routing capabilities by allowing multi-wavelength switching. Fiber delay lines are used to perform optical packet buffering, which accomplishes either input queueing or shared queueing. Here a thorough performance evaluation is carried out with different buffering configurations and the effect of various switch parameters on traffic performance is studied.     

Reliability-constrained dimensioning of transmission resources inpacket-switched networks

The author investigates the problem of dimensioning the transmission resources of a packet-switched communication network satisfying suitable reliability targets. The goal is a communication network providing a minimal transport capability in the presence of failures in network components. This goal is expressed in terms of availability functions to be satisfied by the reliability of communication links. The design procedure is based on the routing of each communication link on more than one transmission path, so that the availability of small shares of the communication link capacity can be increased. An analytic evaluation of the availability figures considered during the design phase is provided and the tools developed are used to compute an end-to-end reliability figure, which also takes into account the amount of user traffic     

Performance analysis of ATM banyan networks with shared queueing.I. Random offered traffic

The paper develops the analysis of multistage banyan interconnection networks in which the switching elements are provided with a buffer shared among all the inlets and outlets of the element. The packet transfer within the network takes place according to absence or presence of backpressure signals between adjacent stages. In this latter case four different modes for operating backpressure have been studied: local and global backpressure with acknowledgment or grant backward signaling. The paper describes three models for the analysis of these networks when loaded by a random traffic. These models are based on an increasing degree of accuracy (and hence of complexity) in the representation of the state of the generic switching elements. The accuracy of these models in evaluating the network performance is assessed in the paper also in comparison with the results given by previously proposed models     

An accurate analytical model on blocking performance of multicast three-stage networks

The fast deployment of broadband networks and the evolution of communication services has revealed the importance of a network-wide availability of multicast communications, that is from one source to multiple destinations. This paper considers three-stage switching networks able to support multicast traffic, i.e. connections in which one inlet of a node is connected to more than one outlet of the node at the same time. An analytical model is developed here that evaluates the blocking probability of multicast connections taking into account statistically the correlation between occupancy events in links belonging to different interstage patterns. Such new model proves to be more accurate than any previous model addressing the same issue. Interestingly enough, unlike other models the new formulation is consistent with the theoretical conditions of a non-blocking three-stage switching network.     

Combined use of finite-state machines and petri nets for modelling communicating processes

In order to model and verify systems of concurrent processes (such as those involved in communication protocols), finite-state machines and Petri nets can be used as local and global models, respectively. The problem of composing a set of communicating finite-state machines into a single global Petri net is considered in the letter with special attention to the case of more than two processes.